Variable capacitors are well known. Capacitors that vary their capacitance with rotation of an armature were used in radio tuners for many years. Combining a capacitor that varies its capacitance with rotation with a capacitance measuring device provides an angular position sensor.
CMOS integrated circuits for measuring capacitance are available from several sources. Micro Sensors of Costa Mesa, Calif. supplies the MS3110 integrated circuit which measures capacitance.
Of the known position sensing means, capacitance sensing is advantageous for being inherently insensitive to temperature, having an inherently linear output, not requiring permanent magnets, and allowing a wide variety of materials to be used in the sensor structure.
Prior to Applicant's invention, no low cost position sensors based on measuring capacitance were suitable for such as throttle position sensing in automobiles. Low cost capacitance position sensing has been limited to micromachined devices such as accelerometers and in diaphragm based pressure sensors in which the deflection of the diaphragm varies a capacitance. One reason sensors such as throttle position sensors and linear position sensors are not based on capacitance measurement is that known low cost capacitance based sensors are very sensitive to movements unrelated to the coordinate of the position being measured such as movements that place parts of the armature closer or farther from the capacitor electrodes.
Accordingly, there is an unmet need for an inexpensive linear or angular position sensor which is responsive by indicating positions along a direction or which indicates an angle of rotation but is unresponsive to other movements.
A reason prior art capacitance based position sensors are responsive to movements unrelated to the coordinates being measured is because such movements usually cause armature tilting, which moves a part of a movable electrical conductor of the armature nearer to one of the fixed capacitor electrodes while moving another part of the same movable electrical conductor nearer to a different fixed capacitor electrode, which greatly affects the capacitance.
Printed circuit boards are made in large numbers by chemically etching copper plated substrate to remove material from areas where conductors are not desired and drilling and plating holes to make connections between conductors on different layers. Turek et al. in U.S. Pat. No. 5,891,528 teaches that printed circuit boards with metallized holes can be formed by plasma spraying a conductive metal after preparing the substrate to keep the plasma sprayed metal from adhering to areas where metallization is not desired.
It is well known to plate metal on plastics by exposing plastic to vaporized metal. Plastics may also be metal plated by chemical vapor deposition as described by U.S. Pat. Nos. 5,191,099 to Gladfelter et al. and 6,399,772 to Shin et al.
A general object of this invention is to provide a low cost sensor offering superior performance and overcoming certain disadvantages of the prior art.